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A056723 Numbers k such that 8*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
1, 7, 23, 29, 133, 173, 367, 1925, 3707, 5765, 9709, 19573, 43753 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Also numbers k such that (25*10^k - 1)/3 is prime.
LINKS
MATHEMATICA
Do[ If[ PrimeQ[ 8*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A095314 A038948 A019389 * A080802 A078515 A225822
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Aug 11 2000
EXTENSIONS
Corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
19573 and 43753 from Serge Batalov, Jan 2009 confirmed as next terms by Ray Chandler, Feb 13 2012
STATUS
approved

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Last modified February 22 18:56 EST 2024. Contains 370260 sequences. (Running on oeis4.)